F.E.A.R. is quite simply one of the smoothest, cleverest, creepiest and most pure-fun games that I've played.
The story carries the action *remarkably* well, and it is peppered with dozens of very tense moments, where you actually may have a hard time pushing forward. (If you weren't armed to the teeth with armor and assault rifles, it may be near impossible) The enemies are well designed enough that their repetition can usually overlooked- and that is actually the largest flaw in this game- its repetition. Levels are mostly claustrophobic, and enemies virtually never vary. But as I said, the shooting and the thick, moody atmosphere certainly eclipse any lack of variation. Guns are very well designed and quite varied. The *feeling* of shooting in this game, as gruesome as it may sound, really is just so much fun. No game that I've played can quite compare. The single player campaign is fun, albeit short. The multiplayer is where you will find excellent replayability, however. Tons of different game modes, great stability and quite balanced gameplay make multiplayer just as fun as its single counterpart.
I could continue about how much fun I've had with this game for a long time, however I will just finish by saying that it is a remarkable achievement, an immensely fun FPS and a real blast to play.